History of In-Floor Heating
In-floor heating, also called radiant floor heating, has been used for centuries. The Romans channeled hot air under the floors of their villas. The Koreans directed hot flue gases under their floors before venting them up the chimney.
In the 1930s, architect Frank Lloyd Wright piped hot water through the floors of his Usonian houses, introducing radiant floor heating to North America.
The “Usonian Homes” were small, single-story houses without a garage or enough storage space. They were L-shaped to fit around a garden terrace, with flat roofs and large cantilevered overhangs for passive solar heating, and natural cooling. In-floor heating was implemented by circulating hot water in copper pipes buried in insulated concrete slabs.
While these homes delivered outstanding comfort for the time, and some are still in use today, others failed early due to chemical reactions within copper piping and certain materials used in concrete. Repeated mechanical strains due to the heating and cooling also produced some failures. These problems finally tarnished the reputation of in-floor radiant heating. By the 1970s, new installs of copper-based radiant floor heating systems were nonexistent.
A lot has changed it the last eighty or so years. Back then, bigger was better, and gas-guzzling was not a concern. As oil grew more costly and even scarce during some years, the industry was required to create cars that were smaller and more efficient.
A comparable progression is occurring in the heating business. As a consequence, the efficiency of the residential furnace has risen dramatically over the last twenty years. As fuel prices continue to escalate, the effectiveness of our heating systems continues to improve.
These days, much of the technology available for in-floor heating is a quantum leap above that available in the past century.
Specially treated polyethylene carries the hot water for hydronic systems, making radiant more affordable than ever. Unlike copper, this inert plastic won’t corrode and can be installed in long runs with just a couple of fittings, reducing the chance of leaks. And with a no-fail track record in Europe going back more than 35 years, it’s also made them more reliable.
Why In-Floor Heating?
Few Canadians don’t relish a warm, comfortable house on a cold winter day. A place that helps them ignore snow, ice and wind as they walk through the door. A place that inspires a sense of well-being and relaxation.
However, ordinary Canadian spends a short amount of time pondering his or her heating system. A lot of us view such systems as essential but boring. When construction budgets are stretched, it is frequently the heating system that gets compromised to save money for other, seemingly more important amenities.
In many cases, it is the homebuilder rather than the homeowner who selects the heating system. Builders are often driven by different priorities from those who will live with, maintain and pay for the operation of that system.
People who have lived with uncomfortable heating systems don’t realize what they have been missing. Many would welcome the opportunity to live in truly comfortable houses and would willingly spend more money, to do so.
Opposite to popular belief, comfort throughout the heating season is not solely defined by indoor air temperature. Comfort is attained and maintained by controlling how our bodies lose heat.
If room conditions allow heat to leave a person’s body at the same rate as it is generated, that person feels comfortable. If heat is released faster or slower than the rate it is produced, some degree of discomfort is experienced.
An average adult engaged in light activity generates heat through metabolism at a rate of about 400 Btu/hr. The body releases this heat through several processes, including convection, radiation, evaporation and conduction.
For indoor environments in colder weather, thermal radiation and convection typically account for almost 75% of the total heat output from the body. Heat loss by thermal radiation alone can be 50% to 60% of the total heat loss, especially within buildings that have a cold wall, floor or ceiling surfaces.
Properly designed radiant in-floor heating systems control the air temperature as well as the surface temperature of rooms to maintain optimal comfort. A hot water heated floor can raise the average surface temperature of rooms. Considering the human body is especially sensitive to radiant heat loss, these warm surfaces notably enhance comfort.
Conductive and convective heat are also contributors to heating with radiant heating systems, and since they emanate from your floor, which is otherwise often cool, it makes for a more comfortable, even heat distribution. Warm feet help make warm homes.
Benefits Of In-Floor Heating Systems
Every heating system affects the health, productivity and general well-being of numerous people over many years. The ability of that system to provide thermal comfort is of paramount importance and should be the primary objective of any heating system designer or installer.
Nothing comes even close to the comfort of an in-floor heating system. The technology works much the same as how the sun warms your body. It’s a natural feel, and you can enjoy a warm chair and heated floors while walking barefoot in the winter.
Several aspects of radiant heating make it more energy efficient.
For starters, the uniform heat distribution over the entire surface of a floor heats the lower half of the room, enveloping inhabitants in warmth at a lower overall temperature—in some cases up to five degrees Fahrenheit cooler—than a conventional heating system.
Hydronic radiant floor systems save energy and lower fuel bills because radiant heat feels comfortable at lower air temperatures, enabling you to lower the thermostat. Further savings can be realized because running a high-efficiency boiler at lower temperatures will increase its lifespan. Besides, hydronic radiant heat is more efficient than other systems because it uses relatively low water temperatures to heat your home.
A distinct advantage for both comfort and efficiency of radiant floor heating is the ability to zone the heat, placing it exactly where it is wanted and needed. Multiple zoning to allow unused rooms to be turned down and use of thermal mass for off peak storage can reduce energy bills.
Radiant heating systems are just about hypoallergenic. Since the air is not forced, you don’t have to be concerned about the heating system distributing pollen, dust and other allergens in the home.
Without blowers, there are no noisy fans, and the home is peaceful.
This underfloor heating system eliminates inconvenient floor and wall registers.
These systems are easy to zone and offer room-to-room temperature control with multiple thermostats.
Radiant systems can use a wide variety of fuel sources to heat the liquid, including solar water heaters, oil boilers, wood-fired boilers or gas boilers.
Forced air systems not only blow hot air, but they also push allergens, dust and other airborne particles to every room in your home. Improved indoor air quality can reduce allergies, medical bills, incidences of asthma and more.
European studies indicate that dust mite populations are reduced as much as 90% in radiant heated homes. And a quiet, peaceful environment, devoid of noisy fans and blowers, is a healthier and more relaxing environment too.
Furniture can be placed anywhere without regard to registers or vents. And rooms with high, open ceilings and floor-to-ceiling windows can be heated easily and efficiently. Mechanical systems for radiant floor heating can also be effortlessly designed because of the ability to interface easily with solar, geothermal and cogeneration fuel cells.
Open doors, large windows and even high air changes will not affect the building’s temperature as much as with a forced air heating system. The heat is retained in the concrete, so the room stays warmer longer without extreme temperature fluctuations. This makes radiant floor heating in concrete slabs ideal for both commercial and residential applications. With the recommended high-density insulation placed below the slab, the floor becomes a large, warm radiator.
HEAT SOURCE OPTIONS
Heat Sources have implications for energy source choice, efficiency and durability. Water heaters can be used effectively as a budget source, but it might be wise to upgrade them to more efficient or reliable heat sources as budget allows. Sometimes heat sources choices are constrained by location.
A wide variety of heat sources can be used with hydronic heating systems. They include gas and oil-fired boilers, hydronic heat pumps and domestic water heaters to name a few. Some are better suited to higher temperature systems while others are ideal for low-temperature systems.
The most common hydronic heat source is a “conventional” gas or oil-fired boiler. They are available with heat exchangers made of cast-iron, steel and finned copper tubing.
The term “conventional” describes boilers that are intended to operate without sustained condensation of the flue gases produced during the combustion process inside the boiler. These flue gases are made up of water vapor, carbon dioxide, and trace amounts of other combustion products depending on the fuels used, and the tuning of the burner.
In contrast to conventional boilers, gas-fired condensing boilers are specifically designed to promote condensation of the water vapor that is produced during combustion. They use large internal heat exchanger surfaces to coax as much heat as possible from the exhaust gases. The heat exchanger surfaces are made of high-grade stainless steel or other special alloys and are not corroded by the acidic condensate that forms as the flue gases cool below the dew point. When properly applied in low-temperature hydronic systems, such boilers can attain an efficiency of 95+ %.
Although they are more complicated and more expensive than most conventional boilers, condensing boilers are well suited for low-temperature hydronic systems such as slab-type floor heating, snow melting, pool heating and low- to medium- temperature domestic water heating. The lower the temperature of the water returning from the distribution system, the greater the rate of condensate formation, and the higher the boiler’s efficiency.
Wall hung boilers when properly applied, can operate with thermal efficiencies in the range of 95% to 98%.
Tank-type Water Heaters
Some hydronic systems can use tank-type domestic water heaters as their heat source. Usually, the size of such systems is limited by the heating capacity of the water heater.
In some systems, a water heater is expected to supply both domestic hot water and space heating. Although possible under some circumstances, the designer must ensure that the heating capacity of the water heater can handle both the space heating and domestic water heating loads. If these loads occur simultaneously, it is usually necessary to make the domestic water heating load a priority over the space heating load.
The preferred approach to such “dual use” systems is to separate the space heating portions of the system from those containing domestic water using a small stainless steel heat exchanger. Because the heat exchanger isolates the space heating components the distribution system must have an expansion tank, pressure relief valve and air separator.
Geothermal Heat Pumps
Geothermal heat pumps are one of the newest heat sources suitable for some types of hydronic heating systems. They extract low-temperature heat from a tubing circuit buried in the earth, or directly from water wells or other sources of water such as a large pond or lake. Using a refrigeration system similar to that in a central air conditioner, the heat captured from the earth is boosted in temperature and then transferred to a stream of water flowing through the distribution system.
Modern homes are well insulated, have excellent glazing, low energy lighting and a variety of other energy efficient solutions to make them seem more like the 40 mpg economy car than the gas guzzlers of the past. But if you add in-floor heating, you can start approaching the ownership of a home that behaves, by comparison, more like a car that gets 100MPG.
We say this not only because of the theoretical savings detailed above, but because we have many homeowners living with the comfort of radiant heat in their homes who report heating bills as much as 60% lower than similar sized homes in the same community. If you might generally expect to pay $2,000 to heat your home through the cold months, bills in the $1,000 range are what many in-floor heating homeowners are experiencing. But remember, your mileage may vary.